A network is used also in a control system for controlling a plurality of controlled devices. For example, in a control system in which one control unit controls a plurality of controlled devices, a plurality of wires for connecting the control unit and the controlled devices are required. In this case, the number of wires increases along with an increase in controlled devices. An increase in wires causes an increase in occupied area, an increase in cost for the wires, and the like. Thus, a request to reduce the number of wires or a request to save wires is made. An example of the control system is an automobile control system. An automobile is mounted with a plurality of sensors and/or actuators, data is collected from the respective sensors thereby to control the actuators. The numbers of sensors and actuators to be mounted further increase along with a recent demand for traveling performance. Consequently, wire harnesses, which are bundles of wires connecting the controlled devices such as sensors and actuators to the control unit, are increased.
In order to save wires, there is described, in PTL 1 and PTL 2, for example, a technique in which a control unit is connected to a plurality of controlled devices via a bus and a network using the bus as a path is configured assuming the control unit and the controlled devices as nodes, thereby reducing the number of wires. A network used in a control system is used under severe circumstances in many cases, and additionally, communication shut-off is not allowed in many cases. Thus, highly-reliable architecture is required. For example, PTL 3 describes a technique for detecting disconnection and keeping communication when a network is disconnected. Further, PTL 4 describes a technique for specifying a disconnected place when a network is disconnected.